This invention is generally directed to toner and developer compositions, and more specifically to developer compositions containing as charge enhancing additives, resin dispersible telomeric quaternary salts. Toner compositions, resin plug pigment particles, and developers, toners plus carrier particles, containing such salts are useful in electrophotographic imaging systems for causing the development of images of high quality for a substantial number of imaging cycles. In one embodiment of the present invention there is provided toner compositions, resin and pigment and developer compositions, toner particles and carrier particles, wherein the toner particles are charged positively, as a result of the presence of the telomeric quaternary salt charge enhancing additive. The charge enhancing additive also functions in a manner so as to increase the admix charging rate of new uncharged toner particles that are added to a charged developer composition.
The electrophotographic process, and more specifically, the xerographic process is well known, as documented in several prior art references. In these processes, an electrostatic latent image is developed by applying electroscopic particles or toner to the electrostatic latent image, using, for example, the cascade development method as described in U.S. Pat. No. 3,618,552, magnetic brush development as described in U.S. Pat. Nos. 2,874,063 and 3,251,706, or touchdown development as described in U.S. Pat. No. 3,166,432. In some instances, it may be desirable in such systems to produce a reverse copy of the original, thus, for example, it may be desired to produce a negative copy from a positive original, or a positive copy from a negative original.
In U.S. Pat. No. 3,893,935, there is disclosed the use of certain quaternary ammonium salts as charge control agents for electrostatic toner compositions. According to the disclosure of this patent, certain quaternary ammonium salts when incorporated into toner materials were found to provide a toner composition which exhibited relatively high uniform and stable net toner charge, when mixed with a suitable carrier vehicle. U.S. Pat. No. 4,079,014 contains a similar teaching with the exception that a different charge control agent is used, namely a diazo type compound.
Many known developer compositions have a tendency to lose their positive charge over a period of time and in some instances, the charge enhancing additives used are incompatible with the thermoplastic resin, thus making it difficult to uniformly disperse or dissolve such materials in the toner composition. Also, the charge control agents as described in U.S. Pat. No. 3,893,935 are soluble in water, causing them to be leeched to the toner surface by moisture, thereby adversely affecting the machine environment, in which they are used and copy quality.
Some recently introduced commercial electrophotographic machines utilize organic photoconductors instead of inorganic photoconductors such as selenium, the organic photoconductors being charged negatively in comparison to selenium, which is charged positively. Accordingly, toner materials containing a positive charge thereon are needed for causing the proper development of images contained on the organic photoreceptor surface. While the prior art describes the use of charge control agents for imparting a positive charge to the toner resin, there continues to be a need for new materials which provide a high positive charge intensity to the toner resin, which intensity is maintained at relatively the same level over an extended period of time. Some charge control agents while they initially impart a positive charge to the toner resin may not be capable of maintaining that charge over a long period of time, and further such charge control agents may be incompatible with the development system, thereby adversely affecting the quality of the images developed. Also some of the prior art charge control agents are incompatible with the toner resin material which adversely affects the charge inducing properties of the charge control agent.
Accordingly, there is a need for toners and developers which can be used in a reversal imaging system, and more specifically, there is a need for positively charged toner materials, which positive charge is substantially high and can be maintained over an extended period of time, thus allowing the production of high quality images, in electrophotographic imaging systems.